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General control line discussion => Open Forum => Topic started by: KEITH McCRARY on January 09, 2019, 11:31:47 PM
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This is a Sig nylon bellcrank. Wire and bushing, no slop. This how I want it. My question is will lubrication negatively affect the nylon ? I have WD40, lithium grease , CRC Heavy Duty Silicone, etc.. What say ye ?
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I glue the 'bearing' piece into the bellcrank, and then sleeve the bearing with brass tube, and polish the pivot shaft (which I assume is steel?). No lube is necessary, and it'll last quite a while.
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Here is some info that I believe regarding lubrication of engineering plastics. (It uses good source material.)
https://www.machinedesign.com/mechanical-drives/engineering-essentials-lubrication-tips-plastic-gears-and-more-part-2
I would not use WD-40. It has a low vapor pressure, meaning that it will evaporate to nothing fairly quickly. At least the carrier will, and I'm not sure about the rest.
They caution that Moly may attack some plastics--but are not specific about which ones.
They do suggest that silicone greases are generally suitable, so of the ones you have listed, I would try some of that, but test the friction to see if you can live with it. All you need is a very thin film.
Delrin is pretty inert, so most things will not readily attack it. The referenced article recommends a synthetic for longer life of the Delrin. I have been known to use Vaseline, a petroleum jelly, which obviously is not a synthetic. I have not had any issues in the past, but now will reconsider my choice....
Thanks for bringing this up,
Dave
Ref.: More info from DuPont on polymer bearings. Bellcranks are low speed (~20 rpm), intermittent motion, small angle mechanisms, but with fairly high loads for their size. (eg. a 1/8" shaft.) The design recommendations are to run against the hardest metal you can, and for it to have the best surface finish possible. The material itself has a magical property that supposedly reduces stiction to a value below running friction, which is really critical for our application. To whatever extent any lubricant would compromise this property, you should avoid that combination. For long life applications, DuPont recommends lubrication. See page 53.
http://www.dupont.com/content/dam/dupont/products-and-services/plastics-polymers-and-resins/thermoplastics/documents/General%20Design%20Principles/General%20Design%20Principles%20for%20Bearings.pdf
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This is a Sig nylon bellcrank. Wire and bushing, no slop. This how I want it. My question is will lubrication negatively affect the nylon ? I have WD40, lithium grease , CRC Heavy Duty Silicone, etc.. What say ye ?
I would be inclined to use nothing, or at most, Singer Light Machine oil. DO NOT use WD-40, Marvel Mystery oil, lithium grease, etc. The nylon will *probably* be OK with these, but, they will all turn to gum and then glue at some later date.
The only good reason to do anything is to keep the pivot wire from rusting, and then abrading the hole.
Brett
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Brett is right on, don't use any type of grease. Just a thin film of silicone on the bearing area on the shaft. You can put a brass bushing on the shaft if needed. The material it's made from (“Rionite” not sure I spelled it right) which is way stronger than most plastics. It was tested to 300 pounds at destruction.
Mikey
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Mikey,
Was it Rynite? That is a PET thermoplastic polyester resin.
Delrin is a type of acetal resin.
Zytel is a nylon resin.
All of these are suggested for use by DuPont as bearing materials. All tolerate dry operation or low/intermittent lubrication.
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I suggest you with very-very good experiences of mine the ZX-100 material.
I found it by an agricultural machine exhibition, and I use it with success since 2000. Minimal friction, no wear, no need for lubrication, and tolerates dust well. Very good vibration damping.
Its pair by me either polished steel, however I paired with hard brass and hard machined aluminum alloy parts, too.
http://www.polyfluor.nl/en/archive/zx-plastics/
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Graphite powder would be my choice, if anything. Since I likely couldn't find the graphite powder I have from Pinewood Derby days, I'd likely use nothing. D>K Steve
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I use nothing but floating. Press fit hard brass bushing in nylon, nothing in fiber.. Fiber washer top and bottom. Polish shaft and wipe with sewing machine oil. Brass washer soldered or Wheel Collars top and bottom. Probably overkill.
Ken
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I have had trouble with control systems getting "stiff" over time. The culprit is usually the flap horn running in brass tube bearings. Easiest fix is to use some sort of penetrating oil, which will wick throughout the brass sleeve bearing.
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I have had trouble with control systems getting "stiff" over time. The culprit is usually the flap horn running in brass tube bearings. Easiest fix is to use some sort of penetrating oil, which will wick throughout the brass sleeve bearing.
The lightest of light machine oils, like the sewing machine oil, is what I use now. I had used air tool oil, but even that gets gummy after a while, and the sewing machine oil doesn't get that way in any practical time frame.
Marvel Mystery Oil, 3-in-1, WD-40, almost any grease, all get gummy over time and bind it up.
If I was making bellcranks like this one, I would use an insert of teflon-impregnated Delrin on a very lightly oiled metal rod, and polish it before installation.
https://www.mcmaster.com/acetal/ptfe
This is what I use on the "teardrop" fitting for the sandwich bellcrank.
Brett